In conventional stepless transmissions, an endless chain is disposed between a pair of V sheaves with grooves of variable width. In speed changing operations, it is usually easier to shift the chain towards the center of the sheave shaft. When the shift is towards the opposite direction, that is, away from the shaft center, it is much more difficult. Since the outward shift of the chain is indebted to the centrifugal force of the rotationary movement, the shift effects more slowly when the system is operating at a low speed, and becomes impossible when the system ceases motion.